Automatic injection devices offer an alternative to manually-operated syringes for administering therapeutic agents into patients' bodies and allowing patients to self-administer therapeutic agents. Automatic injection devices have been used to administer medications under emergency conditions, for example, to administer epinephrine to counteract the effects of a severe allergic reaction. Automatic injection devices have also been described for use in administering anti-arrhythmic medications and selective thrombolytic agents during a heart attack (See, for example, U.S. Pat. Nos. 3,910,260; 4,004,577; 4,689,042; 4,755,169; and 4,795,433). Various types of automatic injection devices are also described in, for example, U.S. Pat. Nos. 3,941,130; 4,261,358; 5,085,642; 5,092,843; 5,102,393; 5,267,963; 6,149,626; 6,270,479; and 6,371,939; and PCT Publication No. WO/2008/005315, all of which are incorporated herein in their entirety by reference.
Conventionally, an automatic injection device houses a syringe and, when operated, causes the syringe to move forwardly and a needle to project from the housing so that a therapeutic agent contained in the syringe is administered to a patient's body. Conventional automatic injection devices include hand-held automatic injection devices and patch pumps, which are self-adhesive, patient-mounted auto-injectors. In use, a patch pump containing a therapeutic agent is mounted onto the body or clothing of a patient and triggered to administer the therapeutic agent to the patient. Conventional patch pumps are typically filled by a patient prior to use. In addition, certain conventional patch pumps have an exposed needle inside the pump, and thus require secondary sterile packaging to maintain sterility.